Insulated electrical conductor and cable



Oct. 16, 1945. J. SHIELD INSULTED ELECTRICAL CONDUCTOR AND CABLE Fildoct.

/N VEN me 'J 5 /ELD m .um

Patented oci. 16,' 194sM UNITED STATES PATENT OFFICE 2,386,753 INSULATEDELECTRICAL CQNDUCTOR CABLE John Shield, Valois, Quebec, Canada, assignorto Western Electric Company, Incorporated, New York, N. Y., acorporation of New York Application October 3, 1942, Serial No. 460,618

3 Claims.

This invention relates to insulated electrical lnductors and cables, andto methods of making It has been the general practice for some time toshield insulated conductors, which were to be used for transmittingaudio frequency currents, from extraneous electric currents ordisturbances in order to avoid interference. In the past, one method ofshielding such conductors has been to apply a braid of metallic wireover the insulation surrounding the conductor. This metallic braid wasexpensive and its application to the conductor was necessarily slow.Whenever a number of conductors in a cable required shielding, theadditional layer of metallic braid over each of the conductors to beshielded naturally inreased the over-al1 size of the cable. Furthermore,the shielding effect of the metallic braid was uniform and could not beconveniently varied, as is desirable in certain instances.v Objects ofthis invention are to produce new and useful insulated electricalconductors and cables, and to provide new and improved methods forproducing them.

An insulated electrical conductor which illustrates one embodiment ofthe present invention comprises a central conductor, a layer ofinsulating material surrounding the central conductor, and a pair ofconductors wound helically over the ltayer of insulating material inopposite direcions.

Other features and advantages of the invention will become apparent fromthe following detailed description thereof, when read in conjunctionwith the accompanying drawing, in which Fig. l is a view in elevation ofan electric cable having portions thereof broken away, and

Fig. 2 is a cross sectional view of the cable taken on line 2 2 of Fig.1.

In the particular embodiment of the invention disclosed in theaccompanying drawing, a plurality of insulated multi-stranded tinselconductors I0, II and I2 are twisted about one another as shown in Fig.l and covered with a sheath I 4 of insulating material, such as rubberor rubber composition, to produce an electric cable: In constructing theconductors I0, II and l2, a plurality of tinsel strands I5-I5 are woundaround with a textile thread and combined with a core cord I6 within acovering I8 of a braided textile material. Over this covering I8 isapplied a`1ayer I9 of rubber insulation.

vIn the particular cable shown, it is desirable to shield only two ofthe three conductors, namely the conductors It and I2. A method ofshielding which illustrates applicants invention comprises winding twoservings of conductors 20--20 in a clockwise direction around each ofthe conductors I0 and I2 which are to be shielded. The conductors 2li-2Uare laid parallel to one another andin an open lay helix about eachinsulated conductor ID and I2, with the lay and number of servings beingadjusted to suit the particular purpose for which the insulatedconductor is to be used. The exact gauge of wire used for the conductorsis not material, but in the disclosed embodiment of the invention, about32 gauge wire is employed. Next, two servings of conductors 2I-2I arewound in a counter-clockwise direction about the insulated conductors I0and I2 and in a manner identical to that in which the conductors 20--20are wound.

After the shielding conductors 2li-20 and 2I-2I have been applied to theconductors I Il and I2, all of the insulated conductors I0, II and I2are twisted about one another and covered with a sheath of insulatingmaterial I4.

An electric cable constructed as disclosed in the above detaileddescription of the particular embodiment of the invention as shown inthe accompanying drawing has been found to operate very satisfactorily.The method of shielding herein described is economical in that itreduces the amount of wire in the shield to but a very small fraction ofthat required to provide a braided shield and may be applied by standardinsulating machines. The rate at which this helically wound open layshield may be applied is about fteen times as great as the rate at whichthe braided wire shield was applied.

When direct current is used, the conductors 2li-2U and 2I-2I may be usedas a return ground conductor. Since the conductors 2U--2ll and 2I-2Itend to sink slightly into the rubber insulation layer I 9, they addvery little to the size of the individual conductors and consequentlyproduce little change in the over-all dimensions of the electric cable.

A particularly advantageous feature of the hereinabove described methodof shielding insulated conductors is the fact that the amount ofshielding may be varied in accordance with re- -quirements for cablesfor speciiic purposes by increasing or decreasing the lay and/or thenumn ber of the conductors 2li-2B and 2I-2I.

The' invention is not limited to the particular embodiment thereofdisclosed in the accompanying drawing, but may take many otherequivalent forms. It is immaterial for the purposes of this inventionwhether or not the conductors shielded are multi-stranded tinselconductors, since conductors comprising but a single wire may besimilarly and equally successfully shielded. The shield composed ofconductors 2li-20 and 2l-2l may be applied with equal eect over rubberinsulation or textile insulation. The number of ductors, as in theformation of a cable. Any or all of the insulated conductors may beshielded Without involving any departure from the present invention.

Other changes and modifications in the particular embodiment of theinvention described herein and illustrated in the accompanying drawingwill be apparent to those skilled in the art.

What is claimed is:

1. An insulated electrical conductor comprising a central tinselconductor, a layer of braided insulating material over the tinselconductor, a. layer of rubber insulation surrounding the layer ofbraided insulating material, a plurality of nne wires wound helicallyand in opposite directions about the rubber insulation of the tinselconductor, the number and lay of the wires being such as to provide a,predetermined degree of shielding of the insulated tinsel conductor.

2. An electric cable comprising a plurality of tinsel conductors, alayer of rubber insulation surrounding each conductor, a plurality ofine wires helically wound parallel to one another in one direction aboutthe rubber insulation of each conductor, a plurality of ne wireshelically wound parallel to one another in a direction opposite to saidmst-mentioned direction, the number and lay of the wires being such asto provide a predetermined degree of shielding of each insulatedconductor, and a covering of rubber insulation enclosing all of theinsulated conductors.

3. An electric cable comprising a plurality of multi-stranded tinselconductors which are twisted around one another, a braid of textilematerial applied over each tinsel conductor, a layer of rubberinsulation surrounding the braid of textile'material on each tinselconductor, a pair of ne Wire conductors Wound parallel to one another inopen lay helixes about the rubber insulation of each tinsel conductors,a second pair of ne wire conductors wound parallel to one another inopen lay helixes about the rubber insulation of each tinsel conductorthat it is desired to shield and in a direction opposite to that inwhich the first-mentioned pair of helically wound conductors are wound,the lays vof the resulting helical' windings being such as to provide apredetermined degree of shielding of the insulated conductors to whichthey are applied, and a covering of rubber insulation surrounding all ofthe conductors.

JOHN SHIELD.

